1. Field of the Invention
The disclosed embodiments of the present invention relate to a calibration method for a communication system and associated circuits, and a non-transitory machine readable medium, and more particularly, to a pre-distortion method for compensating a power amplifier of a radio frequency (RF) circuit having non-linear characteristics and/or memory effect, and an associated apparatus and a non-transitory machine readable medium.
2. Description of the Prior Art
Spectral efficiency has become more significant as a result of wider bandwidth requirements coupled with rapid development in the field of mobile communication. In a complex non-constant envelope modulation, circuit designers have to grasp characteristics of a power amplifier employed in an RF circuit due to the high peak-to-power ratio (PAPR). FIG. 1 is a diagram illustrating a transmitter of a conventional wireless communication system. Non-linear characteristics of a power amplifier 104 may produce amplitude modulation-amplitude modulation (AM-AM) distortion and amplitude modulation-phase modulation (AM-PM) distortion at an output terminal. The distortion will become worse as the bandwidth becomes wider, which make spectral out-of-band re-growth and in-band distortion effects occur. Eventually, the error vector magnitude (EVM) may be degraded. In addition, the output of the power amplifier 104 may be affected by past inputs, which is called the memory effect. The memory effect deteriorates as the bandwidth gets higher. As the conventional pre-distortion circuit 102 cannot handle the non-linear characteristics/memory effect of the power amplifier, it may be unable to satisfy requirements of today's wireless communication systems.